The present invention concerns a pressure wave supercharger with rolling bearings for the rotor according to the main concept of patent claim 1.
The rotors of pressure wave superchargers in practical use in internal combustion engines are all supported in sliding bearings. These sliding bearings are supplied with oil from the lubricating oil system of the engine. Because of the high rotational speed of the rotor, the bearings would be very rapidly destroyed by an interruption of the lubricating oil supply, for example because of a pipe failure, and this represents a danger to operating safety. Because of the substantially greater bearing friction compared with rolling bearings, the driving power is also higher and this leads to higher fuel consumption. Since the lubricating oil must not get into the rotor cells providing the pressure exchange between the induction air and the exhaust gas, contact seals are provided which, however, further increase the necessary driving power and also form a source of trouble. Such seals also have the task of keeping soot-laden exhaust gas, such as appears with diesel engines during idle, part load and changes in load, away from the bearings.
For accurate axial location of the rotor shaft relative to the air and gas casings, which is important for the maintenance of the smallest possible axial play between the rotor end surfaces and the end surfaces of the casings mentioned, sliding bearing systems must have a thrust bearing. In order to avoid jamming of the latter, a certain, relatively large thrust bearing play must be maintained, so that lower limits are set for the rotor play, already mentioned, from this source; it would be desirable to go below these limits in order to reduce the leakage losses.
The use of rolling bearings with permanent grease lubrication permits the reduction of the necessary driving power by more than half and the obviation of continuous oil lubrication excludes the danger of breakdowns due to interruptions in the oil supply. In addition, rolling bearings are characterized by high load carrying capacity and the axial bearing play can be compensated by spring prestressing without, in contrast to sliding bearings, the bearing friction being substantially increased in the process. An economic advantage of rolling bearings is provided by the low manufacturing costs because of the obviation of the elements for continuous oil lubrication and due to the permanent lubrication, which markedly reduces the maintenance costs.
Rolling bearings for pressure wave superchargers have therefore already been proposed, inter alia in Swiss Patent Specification Nos. 349,448, 351,141, 398,185 and 452,280. These bearing systems mainly use voluminous self-aligning roller bearings as the fixed bearing, straight roller bearings being used as well as self-aligning roller bearings as the floating bearing. All these proposals, however, lack measures, which are absolutely necessary, for obviating the danger of sooting of the lubricating grease, which arises due to the pressure difference between the air side hub region of the rotor and the shaft space. They also lack equipment for cooling the rolling bearings, in which substantial quantities of heat can accumulate because there is no longer any oil circulation; these heat accumulations must be removed to the greatest extent possible not only because of their damaging effects on the clearances in the bearing and in the rotor casing, but also in order to avoid a thermodynamic deterioration of the pressure wave process. Investigations have also shown that measures, which provide for a metered continuous supply of grease from the grease store into the bearing, are necessary and the patents mentioned make no provision to this end either.